Caribbean
More ashfall expected in coming days, says MVO
By Government Information Unit
Oct 19, 2009, 13:06 UTC

FLEMMINGS (GIU) – An increase in ashfall is likely in the coming days, says the Montserrat Volcano Observatory (MVO). Friday’s midday report by MVO Director, Dr. Paul Cole said a change in wind direction on Friday morning caused ashfall in Salem, Olveston and Woodlands.

“Activity at the Soufrière Hills Volcano has been at a high level this week with periods of vigorous ash-venting taking place between the night of October 4 until midnight on October 7. Activity was then low until the early hours of October 9 when rockfall activity increased,” the report states.

“Seismic activity this week has been high, with seventy-one volcano tectonic (vt), fifty six rockfalls and forty one long period earthquakes in total.

“The ash-venting events were preceded by a small swarm of twenty-four vt earthquakes starting around 8:45 pm on October 4. There were at least 13 vigorous ash-venting events between 10:00pm on October 4 and 00:01 am on October 7. These events sent ash plumes to between 10,000 and 20,000 ft. Rockfalls and small pyroclastic flows were observed in head of Tyers Ghaut associated with the last three ash-venting events. A helicopter observation flight on the morning of October 7 also revealed fresh rockfall and small pyroclastic flow deposits on the dome talus above Gages, within the chute at the head of the Tar River valley, mostly extending only a few hundred meters from the dome. In the White River valley several generations of pyroclastic flow deposits extended about 1 km south of the dome.

“The average gas flux for the week was 269 tons per day. However, there was a marked decrease in sulphur dioxide flux on the October 2, 3 and 4, with 73, 45 and 108 tons per day respectively, compared with 508 tons per day on October 1. Such a sharp decrease in sulphur dioxide flux has previously been observed associated with the onset of periods of increased activity in May and December 2008. Gas fluxes for October 5, 6 and 7 were higher at 565, 273 and 313 tons per day.

“The activity in the last week appears to have been sourced from the south central part of the lava dome, such that most rockfall/pyroclastic flow activity is concentrated on the southern side and is being channeled into the White River region. However small areas of incandescence have been observed on the north flank of the dome on the evenings of October 7 and 8.

“Although no ashfall occurred in inhabited areas during the ash-venting episodes, a change in wind direction has caused ashfall in Salem, Olveston and Woodlands on the morning of October 9 and further ashfall should be expected in the coming days.

“An increase in volcanic activity could occur at any time and with no warning. Lahars are always a potential hazard in river valleys around the volcano during and after periods of heavy rain.

“The Hazard Level is 3. There is no access to Zone C.”

Additional information on the Soufrière Hills Volcano and the Hazard Level System can be found at the MVO website: http://www.mvo.ms/.